TREATMENT OF WASTE LIQUID

PROBLEM TO BE SOLVED: To stably obtain low cost and high quality treated water by acidifying a waste liquid containing colloidal silica and metallic compounds and then, membrane-separating them to efficiently remove the colloidal silica or the metallic compounds from chemical machinary polishing(CMP) slurry generated in a CMP process. SOLUTION: This CMP slurry is adjusted to a acidic region of a prescribed pH by injecting an acid in a chemical storage vessel 7 in a pH adjusting vessel 5 and is passed through a membrane separation device 6. Then, the colloidal silica as a main component is discharged outside a system as concentrated water. On the other hand, iron salts contained as iron nitrate or iron sulfate are dissociated again to iron ions by adjusting the pH to an acidic region and is permeated through the membrane to be incorporated in permeated water, which is stored in a permeated water tank 8 and is made to flow in a flocculating vessel 1 by a permeated water transferring pump 9. A flocculant such an calcium hydroxide in a flocculant storage vessel 3 is injected to the flocculating vessel 1 by a chemical injecting pump 4 to generate a flock like precipitate in fluorine based waste water to solid-liquid-separate into the treated water and sludge in a sedimentation tank 2.